/Engine/Source/Runtime/Engine/Classes/GameFramework/Character.h
Make the character jump on the next update. If you want your character to jump according to the time that the jump key is held, then you can set JumpMaxHoldTime to some non-zero value. Make sure in this case to callStopJumping()when you want the jump's z-velocity to stop being applied (such as on a button up event), otherwise the character will carry on receiving the velocity until JumpKeyHoldTime reaches JumpMaxHoldTime.
virtual void Jump()